I Want You Back is TWICE's first Japanese digital single, released June 15, 2018 through Warner Music Japan. It is an English-language cover of the Jackson 5's 1969 classic, recorded as the theme song for the Japanese live-action romantic comedy film Sensei Kunshu. Unlike TWICE's other Japanese releases, this was a digital-only single with no physical pressing, making it one of the few releases in their discography with no collectible physical format. A second version of the music video featuring the cast of Sensei Kunshu dancing alongside TWICE was released June 26, 2018. The track was later included on TWICE's 1st Japanese full album BDZ, released September 2018. In 2025 it earned a gold certification from the RIAJ for surpassing 50 million streams in Japan.